Paper & BoardPaper is widely used because it is low cost, holds its shape, and is easily decorated. Commercially-available paper is predominantly made from cellulose fibre from Boxpulped wood, but can also be made from other sources such as cotton, straw, sisal and hemp. All are recyclable.

Paper and board are usually measured by weight or caliper. Material weighing less than 250 grams per square metre (gsm) is referred to as paper, and material at about 250 gsm is referred to as paperboard.

The fibres of machine-made paper run parallel to the length of the machine that produced it. This machine or grain direction affects performance:

Paper tears easiest along the fibres

Folding is easiest along the fibres

Fold endurance is greatest across the fibres

Stiffness is greatest when flexed across the fibres

Paper can also be laminated to increase strength or provide barrier properties. The materials used can be gloss or matt finished or embossed. Other materials can be laminated onto paperboard e.g. foil or plastics.

Commercially-available glass is made from silica, sodium carbonate and calcium carbonate. Other compounds can be added to give colour, sparkle or heat shock Glass jarresistance.

Glass is a popular and useful packaging material because it is:

Inert

Sterilisable

Barrier to moisture and gas

Pressure resistant to a degree

Can be moulded into a variety of shapes

Transparent making the product visible

Glass is also highly recyclable

The most obvious drawback is fragility and the danger of broken glass. The transparency of glass can be a problem where the product is degraded by light.

Glass can be directly decorated but is most commonly labelled.

Metals

The metals used in packaging are predominantly tin-plate or aluminium and are used to make food and drink cans, aerosol cans, tubes, drums and slip or hinged lid Drumsboxes for gift sets and selections of confectionery or biscuits. All packs are recyclable.

Tin-plate is tin-plated steel and the most common material used in food cans. Steel can also be used un-plated or with coatings.

Aluminium is used for drinks cans, closures, trays, tubs and tubes. As foil it can be used in multi-laminate constructions or as a blister pack or container seal.

Metal can be exploited to produce the following packaging characteristics:

Strong and rigid

Barrier to gas and moisture

Pressure resistant

Temperature and pressure resistant / tolerant

Corrosion resistance via coatings

Sterilisable

Directly decorated or labelled

The limitations of metal packaging are in weight and shapes achievable, especially when compared to plastics.

Plastics

Plastics can be used as single materials or in combination. Their properties vary considerably but usually include:

Lightweight

Easily mouldable into almost limitless shapes

Can produce rigid containers or flexible films

Can be impact resistant

Directly decorated or labelled

Heat sealable

The relative disadvantages of plastics are typically polymer specific and the correct choice of polymer can to a practical degree mitigate the weakness. Factors to consider are:

No plastic provides absolute gas and moisture barrier

Plastics melt at temperatures ranging from 650°C to 2,300°C

Chemical resistance varies

Additives in plastics can contaminate some products.

Common plastic polymers used in packaging

Polyethylene (PE)

Low Density (LDPE): used for flexible tubes, film and some bottles. It has a low melting point and as a film relatively poor oxygen and moisture barrier.

High Density (HDPE): widely used for bottles and tubs. Higher melting point but not ovenable. Reasonably wide chemical resistance which can be enhanced by fluorination. Not a sufficient gas barrier for carbonated drinks.

Linear Low Density (LLDPE) Predominantly used as a film or as a sealing layer on multi-laminate materials for bottle seals, sachets, pouches, bags. Available in expanded form for wads.

PolypropylenePolypropylene (PP)Widely used for closures for its ability to form a hinge which resists cracking and splitting. Also used for dispensers, actuators, bottles, jars, cartons, trays and as film on its own or within laminations e.g. crisp bags or pouches. Available in expanded form for tubs and trays.

Typically has higher melting point than PE so although still not “ovenable” it is better suited to hot fill products. Resistant to a relatively wide range of chemicals.

PolyethylenePolyethylene (PE)

This can be subdivided as follows:Low Density (LDPE) for flexible tubes, film and some bottlesHigh Density (HDPE) for bottles and tubsLinear Low Density (LLDPE) as a sealing layer on multi laminate materials for bottle seals, sachets, pouches, bags. Available in expanded form for wads.

Polyethylene terephthalate (PET)

PETWidely used for stretch blown bottles containing drinks, toiletries and food, it has excellent clarity. Also used for jars, tubes and trays.

By far the best gas and moisture barrier of any packaging plastic used for containers it is ideal for carbonated beverages. Its heat resistance makes it suitable for ovenable trays for ready meals.

Polyvinyl chloride (PVC)

Not widely used even though only has a third of its content is derived from oil. It still has a strong presence in vacuum formings used for inserts, clam packs and blister packs, due to its good production line performance. PVC films have excellent stretch and cling properties for hand wrapping fresh produce.

Polyvinylidene chloride (PVDC)

While normally only used in multi-layer films, PVDC has exceptional moisture and gas barrier properties. Many pharmaceutical products could not be packed in blister strips without using PVDC as a layer in the blister film.

Polystyrene (PS)

Mainly seen in its expanded form as protective mouldings for fragile products. Also available as moulded toiletries/cosmetics containers (compacts), some bottles, jars and cups. It has good chemical resistance and excellent clarity although it can be coloured.

Laminates and Co-extrusions

Laminates and co-extrusions are designed to benefit from the properties of two or more materials. Technically laminates are two materials bonded together and co-extrusions are multiple polymers extruded together from molten to form a single piece material.

The following laminates are used widely from sachets through to form-fill-seal cartons such as Tetrapaks:

PE boardPaper (or board) / Polythene (PE)Typically the paper or board gives rigidity and an easily decorated surface while the polythene gives heat-sealability and liquid containment. (But not a barrier in the true sense because water vapour can pass through PE.)

Alu boardPaper or PET / Aluminium foil / PolytheneAgain the polythene provides heat-sealability while the aluminium foil provides barrier properties, with the paper or PET on the outer surface allowing for decoration. PET in particular gives a high gloss finish.

PET/PE-EVOH (ethyl vinyl alcohol)-PEEVOHAs above but for a clear high barrier laminate EVOH is used in place of foil.

Wood

Mostly used for pallets and crates (heavy duty products). Some lidded or hinged boxes are produced e.g. cigars, gifts, tea, cheese. High value spirits use wood and a fewWooden packaging caps incorporate wood.

BambooBamboo

Bamboo is emerging as a packaging material. The illustration shows bamboo cushions for cradling Dell netbooks and laptops.

Cork

Cork has a long history as a packaging material.Cork

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Recent development

Packaging technology has undergone significant development over the last 30 years and materials have been a large driver. The changes mean products can be economically distributed over large geographical areas or stored for reasonable periods without quality loss. Good packaging facilitates cooperation between product, packaging process and material to meet the needs of all stakeholders along the supply chain.

Materials research is leading to different types of biodegradable plastics, improved coatings for better barriers and extended shelf life.

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